You're more likely to get a hip flexor injury if you've had one in the past, you don't warm up properly before engaging in athletic activity, your muscles are already tight or stiff, or your muscles are weak from being overused. If, while exercising, you try to do too much at once in too short an amount of time, you can also put yourself at risk for a hip flexor injury.
The first two weeks of the program are all about lifting heavy with mass-building compound exercises. For everything but abs and calves, reps fall in the 6-8 range; for those accustomed to doing sets of 8-12, this means going heavier than normal. There are very few isolation exercises during this phase for chest, back, shoulders and legs because the emphasis is on moving as much weight as possible to add strength and size.
Firstly, let’s establish where your glutes are and what they actually refer to! Your ‘glutes’ — or your gluteal muscles, as they are more formally known — refer to the muscles in your butt. Specifically, there are three major muscles in this area: your gluteus maximus (the main, large muscle that shapes your backside), your gluteus medius and your gluteus minimus (two smaller muscles that assist the gluteus maximus in moving your body).